Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of the display screen or portion thereof with a graphical user interface showing the claimed design.

The outermost broken lines in the FIGURE show a display screen or portion thereof and form no part of the claimed design. The remaining dark broken lines depicting text and the large circle show portions of the graphical use interface that form no part of the claimed design. The white broken lines do form part of the claimed design. 

CLAIM We claim the ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 